Thiazolo[5,4-d]pyrimidines and oxazolo[5,4-d]pyrimidines can be considered as structural analogues of purines, in which the imidazole moiety is replaced by a 1,3-thiazole or 1,3-oxazole ring system. Although purine chemistry is extensively described in literature, the number of medicinal chemistry papers that describe the synthesis and biological evaluation of oxazolopyrimidines and thiazolopyrimidines is limited. Apparently, the oxazolopyrimidine and thiazolopyrimidine scaffold is not very frequently used in drug discovery programs.
However, biological activities of certain thiazolo[5,4-d]pyrimidines and oxazolo[5,4-d]pyrimidines have been reported. 2,5-Diaminothiazolo[5,4-d]pyrimidin-7(6H)-one, a thio-isostere of 8-amino-guanine, was found to be a weak inhibitor of purine nucleoside phosphorylase (J. C. Sircar et al. J. Med. Chem. 1986, 29, 1804-1806). Thiazolo[5,4-d]pyrimidines were covered by several patent applications as activators of caspases and inducers of apoptosis (WO2008/057402), anti-angiogenic agents (WO2004/01314), growth factor receptor inhibitors (EP1731523), heat shock protein 90 inhibitors (WO2008/059368) and xanthine oxidase inhibitors (WO2007/004688). WO2008/152390 discloses thiazolo[5,4-d]pyrimidines and their use as inhibitors of phosphatidylinositol-3 kinase. WO 2008/005303 discloses vanilloid receptor 1 (TRPV1) modulating thiazolo[5,4-d]pyrimidine analogues and their use for the treatment of diseases, such as pain, arthritis, itch, cough, asthma, or inflammatory bowel disease.
2-Aryloxazolo[5,4-d]pyrimidines have been described as adenosine kinase inhibitors (M. Bauser; et al. Bioorg. Med. Chem. Lett. 2004, 14, 1997-2000). 7-Amino-5-phenylethylamino-2-furyl-oxazolo[5,4-d]pyrimidines act as brain A2A adenosine receptor (A2AAR) antagonists (M. H. Holschbach, et al. Eur. J. Med. Chem. 2006, 41, 7-15). 7-(Substituted-cyclopentyl)aminooxazolo[5,4-d]pyrimidines have been reported to possess tumor growth inhibitory activity (WO/2008/019124). However none of these documents teaches or suggests thiazolo[5,4-d]pyrimidine or oxazolo[5,4-d]pyrimidine derivatives having the substitution pattern disclosed by the present invention and their use as anti-cancer compounds.
A huge number of thieno[2,3-d]pyrimidines is already known in the art. WO 2007/102679 discloses thienopyrimidines with at position 4 a pyrrole-2,5-dione substituent which strongly inhibits IKB kinase-β (IKK-β) involved in the activation of a transcriptional factor, NE-κB, which is associated with inducing various immune and inflammatory diseases, whereby a composition comprising the compound is a useful therapeutic agent against inflammatory diseases, in particular, arthritis and cancer. WO 2007/084815 discloses 2-carboxamide substituted thieno(2,3-d)pyrimidines inhibitors of one or more of the EGFR, HER-2, c-Src, Lyn, c-Abl, Aurora-A or VEGF kinase proteins and the like possessing anti-tumor cell proliferation activity, and as such are useful in treating or ameliorating a EGFR, HER-2, c-Src, Lyn, c-Abl, Aurora-A or VEGF kinase receptor mediated, angiogenesis-mediated or hyperproliferative disorder.
WO 2006/071988 discloses certain 4,5-disubstituted thienopyrimidine derivatives which are useful for the inhibition of PDE10 enzymes, and thus are useful for treating psychiatric or neurological syndromes, such as psychoses, obsessive-compulsive disorder and/or Parkinson's disease. WO 2004/111057 discloses compounds which are particularly useful for inhibiting potassium channels Kv1.5, which are known targets for the treatment of cardiac arrhythmia in the atria such as atrial fibrillation. However, none of these documents teaches or suggests thieno(2,3-d)pyrimidine derivatives having the substitution pattern disclosed by the present invention and their use as anti-cancer compounds.
Marketed drugs with a purine based skeleton are known. Examples include theophylline (drug for the treatment of asthma) and azathioprine (drug for the treatment of transplant rejection). Anti-cancer drugs with a purine scaffold include 6-mercaptoguanine and thioguanine. Purines are also an important constituent of antiviral nucleosides such as acyclovir (used for the treatment of herpes virus infections) and ganciclovir (medication used for treatment of cytomegalovirus infections). Abacavir and dideoxyadenosine (ddA) are both purine nucleosides acting as reverse transcriptase inhibitors and both compounds are licensed as anti-HIV agents.
Purines display a broad range of biological activities and as a result a huge number of purine analogues is already known in the art. WO 2009/005687 discloses purine derivatives and their use as modulators of Toll-like receptor 7. Compounds and pharmaceutical compositions which selectively activate toll-like receptor 7 are useful for treating viral infections in patients. WO 2008/135232 relates to substituted purines and purine derivatives as inhibitors of Aurora A, Aurora B, Aurora C, CHK2, JNK1 α1, JNK3 and abl kinase. These compounds possess antiproliferative properties and are useful in the treatment of proliferative disorders such as cancer, leukemia, psoriasis and the like. WO 2008/094737 discloses purine derivatives as inhibitors of calcium dependent protein kinase 1 (PfCDPKI). These purines are useful for treating malaria. WO 2008/090181 relates to a new series of purine derivatives as inhibitors of Janus kinases. JAK3 kinase inhibitors have been recognized as a new class of effective immunosuppressive agents useful for transplant rejection prevention and in the prevention or treatment of immune, autoimmune, inflammatory and proliferative diseases such as psoriasis, psoriatic arthritis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel diseases, systemic lupus erythematosus, type I diabetes and complications from diabetes, allergic reactions and leukemia. WO 2008/060301 also discloses 7-substituted purine derivatives as immunosuppressive drugs useful for treatment of an autoimmune disease, an inflammatory disease, a mast cell mediated disease, hematological malignancy and organ transplant rejection. However none of these documents teaches or suggests purine derivatives having the substitution pattern disclosed by the present invention and their use as anti-cancer compounds.
However there is a continuous need in the art for specific and highly therapeutically active compounds, such as, but not limited to, drugs for treating cancer such as leukemia. In particular, there is a need in the art to provide anti-cancer compounds, which are active in a minor dose in order to replace existing drugs having significant side effects and to decrease treatment costs.
Accordingly, in view of the relatively few choices for anti-cancer agents effective in low doses with low toxicity profiles and manageable side effects, there exists a need in the art for identification of alternative agents for several proliferative disorders such as cancer.